I would guess that if you are reading this you already have a grasp on basic soloing concepts and do your thing by ear, which in most cases is fine and will yield good results. However, when delving into more complex progression its often the case that you may play notes that don't quite take you anywhere and sometimes even sound completely off place. You might wonder how the guitar greats breeze through progressions playing all sorts of scales and arpeggios and yet their solos flow and captivate their listener.
Chord tone soloing in the basic sense is playing melodies based of the notes that make up the chords in the underlying chord. The chord tones are therefore the tonic(root), third and fifth of the chord (note: if your chord has more than 3 notes, the remaining notes are also chord tones). Thus, if you are taking a chord tone approach to soloing you might play licks the revolve around these notes.
The basic idea is to play around and ending on the chord tones of each chord in the progression, but you might also add notes that complete a chord - for example, you might play a C over a Bbm7 (T-Bb b3-Db 5-F b7-Ab) chord which would in turn create a Bbm9 chord.
Before we start working on this I would suggest having either a drum machine, a program such as Guitar Pro or digital recorder of some kind so that you can record/program in the progression I will show in this lesson. If you do not have this, have someone strum out the chords while you practice. Also do not be alarmed if this is an odd key to you as I picked it because it will help those that have the habit of playing in Em get away from playing the same licks.
So, let us get started:
First we will look at a simple two chord progression borrowed from a 12 bar blues in the key of Bb.

|:----Bbm7(I)----|----Ebm7(IV)----|----Bbm7(I)----|----Bbm7(I)----:|

Program in/Record this progression in whatever style/groove you like. I'd suggest something like a funky rock or Latin rock.
Before you start shredding over this progression let us first analyze the chords in it so that we know what to play and when to play it.

At a first glance, you will notice that there are two notes these chords share with each other - Bb and Db. This means that these two notes are "safe notes" for both of these chords. In addition, playing these notes does not "sound out" the underlying chord so they can be used when you want your solo to remain static.
But what about the remaining notes in each chord?
Well, the remaining notes in each chord are what tells us what to play over that chord.
Bbm7 has the notes Bb, Db, F and Ab. Let us look at the Bm Natural Minor scale for a second - Bb C Db Eb F Gb Ab Bb. Comparing the notes in Bbm7 with the Bb minor scale we quickly notice that we have the 1, the b3, the 5 and the b7 of Bb minor. Wow, wait a minute that is one note short of the Minor pentatonic, add in the 4 and there it is. Thus, its safe to assume that whenever there is a Bbm7 in that progression we can play Bb minor pentatonic licks over it!
Now, looking at Ebm7 we have the notes Eb, Gb, Bb and Db. Again, if we compare that to Bb minor scale - Bb C Db Eb F Gb Ab Bb you will notice that Ebm7 has the 1, the b3, the 4 and the 6 of Bb minor scale. However, in this case, the root of the chord is the 4 of the scale. The approach in this chord is a little different than the approach taken for Bbm7: you might play the entire Bb minor scale but focus on bringing out that Gb that is not present on the Bbm7. Well what about the Eb? The Eb is the root of the underlying chord and as such it is a somewhat colorless note, it is also present in Bb minor penta, which we pretty much established is the way to go over Bbm7.
Alright, now that we know what we can play, Bb minor penta over Bbm7 and Bb natural minor over the Ebm7, we can finally get to the fun part.
The idea is to build your solo using this concept so to start off, force yourself to use this pattern over Bbm7

Experiment with this for a a few choruses. Once you feel you are getting somewhere then we can start building a full blown solo. Doing that is entirely up to you and changes as you play different styles and with different musicians, but a good way to do this is to take a "storytelling" approach. This means that we are building a solo that has a start, a ramp in "tension", a climax and finally resolution. For the first couple of choruses you might focus on these small patterns, making short, melodic phrases. Then, as tension builds you start ending more notes, using repetition, and playing higher up in the neck. Then you might start playing even more notes and faster runs. Finally when the tension is true the roof you release all of it by landing on a screaming bend lick based of the root of the I chord as the rest of the band scales down and voila! You've got yourself a solo.

Now that is an introduction to chord tone soloing, it is not much but you will be surprised at what it can do to your playing if you practice it. If you have any questions, send me a PM on the forums or post on the comment box and I'll get to you in time. Also, depending on how well this lesson is rated I might even do a second lesson on chord tone soloing with more involved progressions. For the mean time, this is it...

If you guys think that Bb is hard/bad, that's just a tad odd. You don't need an open low E for every song. I play things in Fm (4 flats, Bb Eb Ab Db) in standard and it doesn't bother me in the slightest. I think it just takes some getting used to.